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July 30, 1963
T. c. T. NEW ET AL
3,099,583
FORMATION OF SEMICONDUCTOR TRANSITION REGIONS
BY ALLOY VAPORIZATION AND DEPOSITION
Filed March 11, 1959
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WITNESSES:
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INVENTORS
Thorndike C.'[ New and
James Poppus.
BY _
United States Patent 0 ice
3,09%,588
Patented July 30, 19%3
2
1
snaasss
FORMATION OF snrarcorsnucron rnANsrrroN
REGIONS BY ALLOY VAPQRHZATION AND
DEPGSITION
‘Westrnore
Thorndike C. T. New, Hemp?eld Township,
land County, and James Pappas, North Huntingdon
assignors to
Township, ‘Westmorelaud County, Pan,
East Pittsburgh,
Westinghouse Electric Corporation,
Pa” a corporation of Pennsylvania
Filed Mar. 11, 1959, Ser. No. 79%,é4i8
6 Claims. (Cl. 148-215)
dium will melt inside the aluminum shell. When the
remainder of the aluminum melts a miscible alloy is
formed.
More speci?cally and with reference to FIG. 1, there
is illustrated a capsule or pellet 10 comprising a shell 12
of aluminum and a core 14 of indium.
The pellet 10
may comprise from 90% to 10% by weight of alumi
num and from 10% to 90% by weight of iridium.
One particularly satisfactory method ‘for preparing the
doping ‘alloy pellet 10 comprises taking a rod of solid
10 aluminum and drilling a passageway partially there
throu-gh.
The passageway is then ?lled with indium,
This invention relates to a process ‘for the fabrication
silver or a mixture thereof and the open end of the pellet
of semiconductor devices and more particularly to a proc
pinched shut or plugged or otherwise closed.
ess for fabricating a semiconductor ‘device by the vapor
The pellet 10 of FIG. 1 is employed in a vacuum vapor
deposition of a doping alloy upon the surface of ‘a semi 15 depositing apparatus. With reference to FIG. 2 there
conductor material.
is illustrated a vacuum evaporization bell jar furnace 16
'In the past attempts have been made to alloy ‘aluminum
comprised of a metal base 18 which supports a glass bell
to semicondnctive materials, particularly germanium, to
jar 20. A close fit between the glass bell jar 20‘ and the
‘form an emitter of high efliciency. It is however difficult
base 18 is assured by disposing the jar 20 in a groove 22
to solder additional connections to aluminum. Attempts
containing a sealing material in base 18.
have been made to overcome this di?iculty by evaporating
The base 18 has a port 26 through which the interior
a second metal, for example, silver, over the aluminum.
of bell jar 20 of furnace 16 may be evacuated. A ?rst
The shortcomings of this method are well known to those
heating means 28 is disposed in the lower portion of the
skilled in the art.
furnace, and a second heating means 30 is disposed in
An object of the present invention is to provide an
the upper portion of the furnace. A support member 32
improved process for the preparation of ‘a semiconductor
having an aperture or passageway 33 therethrough is dis
device by vapor depositing ‘from a single container an
posed in the upper portion of the furnace in close asso
aluminum-indium doping alloy upon a surface of a body
ciation with the heating means $0.
of semiconductor material.
In carrying out the process of this invention, the doping
Other objects of this invention will, in part, appear 30 ‘alloy pellet 10 placed in a graphite boat 34 is disposed
hereinafter and will, in part, be obvious.
on the ?rst heating means 28. A water of a semicon
For a better understanding of the nature and the ob
ductor material 36, for example, a wafer comprised of
jects of the invention, reference should be had to the fol
silicon,
germanium, indium-arsenide, gal-lium-phosphide,
lowing detailed description and drawings, in which:
silicon carbide, or the like is disposed on the support
FIGURE 1 is a view in cross section of a pellet of 35 member 32. However, for the purpose of clarity, the
doping alloy components suitable for use in accordance
invention will be described in terms of a germanium
with this invention;
wafer. The furnace is evacuated to a pressure of 10*4
FIG. 2 is ‘a vertical cross section of ‘a bell jar ‘furnace
or less mm. of mercury by evacuating the air out through
suitable for use in accordance with this invention;
port 26 by a suitable means (not shown).
110
FIG. 3 is a vapor phase diagram of an ‘aluminum indi
The heating means 28 is energized and the graphite
um alloy suitable for use in accordance with the teaching
boat and the pellet 10 are heated rapidly. Because of
of this invention; and
-
FIG. 4 is a side view in cross section of a semiconductor
the difference in melting points, the indium (M.P. about
155° C.) melts ?rst but is held within the aluminum
device prepared in accordance with the teaching of this
shell until the shell melts. As the temperature rises, the
45
invention.
‘aluminum and indium pass through the various stages
In accordance with the present invention and attain
set ‘forth in the aluminum-indium phase diagram of
ment of the foregoing objects, there is provided a process
for forming a semiconductor device which comprises
FIG. 3.
As the temperature reaches the range of ap
proximately 900° C. to 1100° C. (depending on the
vapor depositing a readily solderable homogeneous dop
originm composition of the pellet 10‘) ‘a homogeneous
50
ing alloy, the major component being aluminum and the
liquid results. From this homogeneous liquid a homo
minor component being indiurmupon a body of a semi
geneous vapor is evolved ‘and is allowed ‘to contact the
conductor material While maintaining the body of the
surfaces of wafer 36, exposed through passage 33.
semiconductor material at a temperature above the solidus
Initially, the wafer 36 is kept at a temperature below
temperature of the eutectic of the aluminum with the 55 the melting point of germanium and aluminum but above
the solidu-s of the aluminum-germanium system, for ex
semiconductor material, and below the melting point of
ample, within a temperature range of 425° C. to 650° C.
the aluminum.
by heating means 30‘. As a result, the initially deposited
It has been discovered that if aluminum and indium
aluminum, for example, from 0.0001 to 0.005 inch in thick
‘are melted in such fashion that a miscible solution of
‘aluminum and indium is produced, the vapors from such 60 ness will alloy with the germanium "and form an alumi
num rich germanium alloy solution. Thereafter, while
a solution will have a composition correlated to the
the evaporation process is continued, the germanium
liquid composition.
wafer is allowed to cool down slowly below the germani
It has been discovered that if a closed capsule of
um-aluininum eutectic temperature and a thin layer of
aluminum ‘containing a core of indium is heated the in
assasss
aluminum rich germanium of p-type semiconductivity
crystal is regrown from the surface of the body of the
original wafer to form a desired junction. Subsequently,
the aluminum deposited upon the germanium layer is in
the solid phase. The indium, being immiscible, tends to 5
separate out and remains in a liquid phase distributed as
very fine droplets but the resultant deposit comprises a
solid aluminum matrix which interlocks the indium.
Thus, von cooling below 155° C., a metastable alloy is ob
tained on the surface of the water 36.
With reference to FIG. 4, there is illustrated a semi
conductor element 4t} prepared as described above. Ele
ment 40 is comprised of an n-type germanium wafer 42,
a p-type layer 44 resulting from the doping and regrow
ing of the germanium 42 and a layer of aluminum-indium
metastable alloy 46 which is comprised of aluminum
matrix 48 and disposed phase of indium St}.
A structure such as that shown in FIG. 4 can be easily
soldered due to the presence of the indium in the alloy
layer 46‘.
The following examples are illustrative of the practice
of this invention.
Example I
A capsule pellet, similar to that illustrated in FIG. 1
and comprising 75% by Weight aluminum and 25% by
Weight indium, was prepared by drilling a 1,56 inch diam
eter passage having a length of 9/16 inch in an aluminum
rod having a diameter of 14; inch and a length of 5/8 inch.
The passage was ?lled with a predetermined amount of
indium and the end of the rod pinched over ‘to seal the
indium within the aluminum. The pellet was comprised
of 75% by weight, aluminum and 25%, by Weight, indium.
The pelletthus prepared was placed in a graphite boat
the doping alloy being deposited simultaneously upon the
body ‘whereby, an aluminum rich region is formed with
in the body of semiconductor material, said aluminum
rich region converting a portion of the body to a p-type
semiconductivity, and a layer of metastable alloy com—
prised of indium and aluminum is formed on the outer
surface of the aluminum rich region.
2. A process for forming a semiconductor device which
comprises vapor depositing a homogeneous vapor from
a single homogeneous melt comprised of an alloy compris
ing from 10% to 90%, by Weight, aluminum and from
90% to 10%, ‘by weight, of indium, upon a body of n-.ype
semiconductive material selected from the group consist
ing of germanium ‘and silicon, in a vacuum while main
taining the body of n-type semiconductive material at a
temperature below its melting point, ‘below the melting
point of the aluminum and above the melting point of the
indium, the aluminum and indium comprising the doping
alloy being deposited simultaneously upon the body where
by, an aluminum rich region is formed within the body
of semiconductor material, said aluminum rich region
converting a portion of the body to a p-type semiconduc
tivity, and a layer of a metastable alloy comprised of in
dium and aluminum is formed on the outer surface of the
aluminum rich region.
3. A process for forming a semiconductor device which
comprises preparing a homogenous melt of aluminum and
indium of a predetermined composition, vaporizing the
homogeneous melt, whereby a homogeneous vapor of
aluminum and indium is formed, collecting the homo
geneous vapor upon body of n-type semiconductive mate
rial 'while maintaining said body at a temperature below
its melting point, below the melting point of aluminum
and with an n-type germanium wafer was placed on a
and above the melting point of indium, and then con
masking frame in a furnace similar to that illustrated in
FIG. 2.
to cool to a temperature below that of an eutectic of
The furnace was evacuated to approximately 16‘4 mm.
of mercury.
The n-type germanium wafer was maintained at a tem
perature in the range of approximately 500° C. while
the alloy pellet was rapidly heated to a temperature in the
range of approximately 1030‘0 C. whereupon a homogene
ous indium aluminum liquid resulted. A homogene
ous vapor comprised of 90% ‘by Weight aluminum and
10% by Weight indium rwas evolved and allowed to con
tinuing the collecting of vapor ‘while allowing the body
aluminum and the n-type semiconductive material, where
by, an aluminum rich region is formed within the body of
semiconductor material, said aluminum rich region con
verting a portion of the body to a p-type semiconductivi-ty,
and a layer of a metastable alloy comprised of indium and
aluminum is formed on the outer surface of the aluminum
rich region.
4. A process for forming a semiconductor device which
comprises vapor depositing 1a homogeneous vapor of alumi
tact selected surfaces on one face of the n-type germanium
num and indium from a single homogeneous melt com
wafer and collect thereon. After approximately three
minutes the germanium n-type wafer was allowed to cool
to a temperature of about 350° C. to 400° C., germanium
redeposited from the aluminum-indium layer upon the
prising an alloy comprising 75% by Weight aluminum and
25% by weight indium upon a body of n~type germanium
wafer thereby forming a p-type semiconductivity layer.
A metastable aluminum indium layer was deposited over
this germanium layer.
Example 11
A germanium transistor was prepared wherein the emit
ter was made by the technique set forth in Example I. It
was tested and found to have an average current gain of
63 at 1.5 amperes collector current.
while maintaining the n-type germanium at a temperature
eloW its melting point, below the melting point of alumi
mum and above the melting point of the indium, whereby,
an aluminum rich region is formed within the body of
semiconductor material, said aluminum rich region con
verting a portion of the body to a p-type semiconductivity,
and a layer of a metastable alloy comprised of indium and
‘aluminum is formed on the outer surface of the aluminum
rich region.
5. In a process for preparing a semiconductor device
from a body comprised of n-type semiconductive material
60 selected from the group consisting of silicon and ger
While the invention has been described with reference
manium, the steps comprising forming an emitter by de
to a particular embodiment and examples thereof, it will
positing upon one surface thereof an evaporated layer of
be understood, of course, that modi?cations, substitutions
a doping alloy from a single homogeneous melt comprised
and the like may be made therein Without departing from
its scope.
of aluminum and indium, the aluminum and indium com
We claim as our invention:
prising the doping alloy ‘being deposited simultaneously
1. A process for forming a semiconductor device which
upon the body whereby, an aluminum rich region is
comprises vapor depositing a readily solderable homo
geneous doping ‘alloy comprised of aluminum and indium
formed within the body of semiconductor material, said
aluminum rich region converting a portion of the body to
from a single homogeneous melt, upon a body of an n
a p-type semiconductivity, and a layer of a metastable
of n-type semiconductor material at a temperature below
alloy comprised of indium and aluminum is formed on
the outer surface of the aluminum rich region.
its melting point, below the melting point of the aluminum
component of the doping alloy and above the melting
point of indium, the ‘aluminum and indium comprising
from a ‘body comprised of n-type semiconductor material
selected from the group consisting of silicon and ger
type semiconductive material while maintaining said body
6. In a process for preparing a semiconductor device
manium, the steps comprising forming an emitter by de
3,099,588
positing upon one surface thereof an evaporated layer
of a doping alloy from a single homogeneous melt com
prised of from 10% to 90% aluminum and from 90% to
10% indium, the aluminum and indium comprising the
doping alloy being deposited simultaneously upon the
body whereby, an aluminum rich region is formed Within
the body of semiconductor material, said aluminum rich
region converting a portion of the body to a p-type semi
conductivity, ‘and a layer of metastable alloy comprised
of indium and aluminum is formed on the outer surface 10
of the aluminum rich region.
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,464,821
2,695,852
2,845,894
2,861,018
2,870,049
2,870,052
2,873,222
2,879,188
2,909,453
Ludwick et a1 _________ __ Mar. 22,
Sparks ______________ __ Nov. 30,
sMcIlvaine ____________ __ Aug. 5,
Fuller et a1. _________ __ Nov. 18,
Mueller et al __________ __. J an. 20,
Rittman _____________ __ Ian. 20,
Derick et al. _a ________ __ Feb. 10,
Stnull _______________ __ Mar. 24,
Losco et ‘a1 ____________ __ Oct. 20,
1949
1954
1958
1958
1959
1959
1959
1959
1959